Impact

Attackers can specify a specific string of characters, which would confuse the bridge into combining an attacker-owned channel and an existing channel, allowing them to grant themselves permissions in the channel.

Patched

The vulnerability has been patched in matrix-appservice-irc 0.35.0.

Workarounds

Disable dynamic channel joining via dynamicChannels.enabled to prevent users from joining new channels, which prevents any new channels being bridged outside of what is already bridged, and what is specified in the config.

References

• https://matrix.org/blog/2022/09/13/security-release-of-matrix-appservice-irc-0-35-0-high-severity

Credits

Discovered and reported by Val Lorentz.

For more information

If you have any questions or comments about this advisory email us at security@matrix.org.

References

• GHSA-xvqg-mv25-rwvw
• https://nvd.nist.gov/vuln/detail/CVE-2022-39203
• https://matrix.org/blog/2022/09/13/security-release-of-matrix-appservice-irc-0-35-0-high-severity/